Vacuum pumping system



Nov. 14, 1933. J. c. READ 1,935,415

VACUUM PUMP ING SYSTEM Filed Sept. 16, 1952 Invent or: John C Read,

H is Attorney.

pipe communicates with this trough.

Patented Nov. 14, 1933 1,935,415- VACUUM PUMPING SYSTEM John C. Read, Rugby, England, assignor to General Electric Company,

New York a corporation of Application September 16, 1932, Serial No.

3 Claims.

This invention relates to vacuum pumping systems such as are used in connection with mercury arc rectifiers and the like.

In such systems when high pumping speeds are 5 to be obtained it is necessary to reduce to a minimum the frictional resistance in the pipe connecting the rectifier chamber to the mercury vapor vacuum pump and this is generally accomplished by making the connecting conduit as short 0 and of as large a cross-sectional area as practicable. With this arrangement however there is always the danger that mercury will gradually distil over from the pump to the rectifier or vice versa ultimately causing the pump to cease functioning correctly.

The object of this invention is to provide a method for maintaining the correct mercury level in the boiler of a mercury vapor vacuum pump.

To that end thisinvention consists in providing an overflow pipe leading from the boiler of the mercury vapor pump and so arranged that when the mercury in the boiler rises to its correct level any surplus mercury entering the boiler will overflow back into the rectifier. To ensure that the mercury in the boiler is kept at its proper level the vacuum pump and the main vacuum pipe may be kept at a lower temperature than the rectifier. An annular trough is provided round the interior wall of the main vacuum pipe and the overflow mercury condensed on the walls of the main vacuum pipe runs down and is collected in this trough and passes through the overflow pipe back to the boiler if the level in this is below the level of the mercury in the trough. Should the level of the mercury in the boiler be correct, surplus mercury in the trough will overflow into the rectifier. The overflow pipe may be made U-shaped so that heat is not taken from the boiler by convection currents in the mercury in it. j

My invention will be better understood from the following description when considered in connection with the accompanying drawing in which one embodiment of my invention is shown and its scope will bepointed out in the appended claims. In the drawing the casing of the mercury pump, containing the nozzles and water jacketing arrangement, is shown at l. The pump extracts air from the rectifier 2 through the suction pipe 3 .which is made as wide and short as possible in order to obtain the maximum possible pumping speed. The air is expelled from the mercury pump towards the rough vacuum pump (not shown) through the outlet pipe 4. The mercury boiler 5,

which may be heated in any convenient manner,

and in Great Britain October 10,

such as by induction by means of the transformer core 6 passing through it, should have its mercury level '7 kept approximately at a constant level. the collecting trough 9 in the main suction pipe 3. The suction pipe is provided with a water jacket 10 which cools the region of the collecting trough and also a considerable part of the pipe above the latter. The suction pipe and the mercury pump are maintained at a temperature generally below that of the rectifier, so that there is a tendency for mercury to distil over slowly into them. Some of the mercury condensed in this way will condense 7 in the pump itself but most of it will condense in the water cooled section of the suction pipe and will run down into the collecting trough. Consequently the collecting trough will tend to remain always full and surplus mercury will run over, back into the rectifier. Due to the connecting pipe 8 the mercury level in the pump will be maintained at a level governed by the level at which the mercury overflowsfrom the trou h 9.

It is essential that there shall be no rapid evaporation of mercury from the trough 9 due to heat transmitted to it from the mercury boiler.

For this reason the connecting'pipe 8 is made small and fairly long, and may be water cooled as by a water jacket'll at the end remote from the boiler; and this pipe on leaving the boiler at first turns downwards to au-shaped depressionv 12 so that hot mercury from the boiler is, not able to rise upwards in the pipe 8 and thereby transmit heat to the trough 9 by convection currents. i

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a vacuum pumping system for a mercury vapor device, a vacuum suction pipe connected to said device, a mercury pump connected to said suction-pipe, a mercury collecting trough mounted in said suction pipe, and means to maintain the mercury in said trough and said pump at substantially the same level, said means comprising an overflow pipe connected to said trough to conduct mercury between said pump and said f trough.

2. In a vacuum pumping system for a mercury vapor device, a vacuum suction pipe connected to said device, means to circulate a cooling medium in contact with a section of said pipe, a mercury pump connected to said suction pipe, a mercury collecting trough mounted in said section of said pipe, and means to maintain the mercury in said trough and said pump at substantially the same level, said means comprising an overflow pipe For this purpose a small pipe 8 is led to 60 connected to said trough to conduct surplus mercury between said pump and said trough.

3. In a vacuum pumping system for a mercury vapor device, a vacuum suction pipe connected to said device, a mercury pump connected to said suction pipe, a mercury collecting trough mounted in said suction pipe, and means to maintain the mercury in said trough and said pump at JOHN c. READ. 

